Retorts for the production of alkaline earth metals



H. G. WARRINGTON Erm.. 2,829,878 RETORTS FOR THE PRODUCTION O F ALKALINE EARTH METALS April s, 195s vFiled Dec. 13, 1955 UnitedStates Patent O RETORTS FOR THE PRODUCTION OF ALKALINE EARTH METALS Harold G. Warrington, Toronto, Ontario, and Donald J.

McPhail, Haley, Ontario, Canada, assignors to Dominion Magnesium Limited, Toronto, Ontario, Canada Application December 13, 1955, Serial No. 552,925 3 Claims. (Cl. 263-47) posed end condenser section through which the retorts are charged and discharged. The furnace is maintained at a substantially constant temperature but during the charging and discharging of the retorts the metal of the retorts is subjected to temperature changes which impose stress on the metal. During the reducing operation a reduced pressure is maintained in the retorts. These factors coupled with the relatively high furnace temperature cause the retorts to have relatively short useful life which adds to the cost of producing the desired alkaline earth metal. When a retort partially collapses it may be restored to original shape by compressed air.

In attempting to effect improvements retorts have been used having a heated length of 5 to 9 feet, an outside diameter of 7.5 to 14 inches and a wall thickness of "A to 19/32 inches. The yield of metal is substantially proportional to the length vof the heated section of the retort.

It has been found that a retort having a wall thickness less than one-thirteenth of the resist collapse by creep of the metal within a reasonable period and that when the wall thickness exceeds one-tenth of the outside diameter of the retort there is a decrease in yield of metal produced in a given time.

The object of the present invention is to improve the specic construction of the retort to insure a longer useful life and a higher production yield of metal from the retort.

In accordance with the present invention these metal retorts are cast, preferably centrifugally, and internally machined to provide a uniform ratio of outside diameter of the retort to its wall thickness which may vary between 10.2 and 13.0. When so made the retorts have a consistently longer life and give optimum metal recovery.

Several factors account for the improvement. Centrifugal castings of the retort tends to concentrate lighter parts of the molten metal, such as slag, dross oxide and porosity on the inner wall of the retort. When this inner Ilayer is removed the retort is stronger than that obtained by casting to similar dimensions. The retort has a more uniform wall thickness. There is thus less distortion of the retort in operation in the furnace and when a partially collapsed retort is restored to its original shape by compressed air the response is more uniform. In using the retorts the sintered and fritted reaction residue which adheres to the retort wall in the form of cake is more readily removed from the machined surface than from an as-cast surface. The passage of heat to the charge is improved. The important practical advantage is that the capacity of the retort to produce metal during its useful life is increased by about over that 2,829,878 Patented Apr. 8, 1958 obtained when using cast retorts having a ratio of outsidediameter to wall thickness of 10.0 which gave the best retort life consistent with optimum metal recovery.

In the accompanying drawings,

Fig. 1 is a sectional elevation of a retort for use in the thermal reduction of alkaline earth metal oxides.

Fig. 2 shows graphs of the outer diameter to wall thickness ratio plotted against metal yield per foot of retort length for both optimum charge weight and constant charge weight.

Referring to Fig. 1 the retort 1 has an elongated cylindrical wall portion 2, an end portion 3 integral with said wall portion 2 and a condenser section 4 having a removable closure 5. The condenser section 4 has a 6 therearound and an outlet 7 from the retort may be drawn. diameter O. D. and a wall thickand shows a comparison between the optimum charge weight and a constant charge weight. It is observed that as the O. D./T ratio increases the charge weight may also increase. From the graph it may be seen that the most effective range lfor the O. D./T ratio is from 10.2 to 13.

For use in other than an inert atmosphere the retort should be made of some type of stainless steel such as If the external surface of the retort is in an inert atmosphere or vacuum then the retort material may be a mild steel. The optimum heated length of retort is in the range of about to 120 inches. The best outside diameter of the retort may vary slightly according to the particular alkaline earth metal being produced within the range of 12" to 16". Mg and Ba have the Optimum retort O. D. in the range l2" to 14 and Ca and Sr in the range of 121/2 to 16".

It is essential that the external surface of the retort be free from dross, casting scale or casting skin which has been found detrimental to satisfactory metal yields and promotes early retort failure. The improved results, therefore, have only been achieved by a retort the inner wall of the heated length of which is free from dross, casting scale or skin.

What is claimed is:

1. A metal retort for the production of alkaline earth metals by thermal reduction under reduced pressure, adapted to resist collapse in a heatingfurnace which retort to its wall thickness being 10.2 to 13.0 the reducing portion of the retort being at least 90 inches in length and having an outside diameter not substantially less than 12 inches.

2. A metal retort for the production of alkaline earth metals by thermal reduction under reduced pressure, adapted to resist collapse in a heating furnace which comprises a centrifugally cast elongated cylinder having an integrally formed closure at one end and a removable closure at the other end, the internal surface of the retort being free from dross and the ratio of outside diameter of the retort to its wall thickness being 10.2 to 13.0 the reducing portion of the retort being at least 90 inches in length and having an outside diameter not substantially less than 12 inches.

productionA of alkaline earth y diameter Yof the cylinder to its wall References Cited in the le of this patent UNITED STATES PATENTS Millholland July 15, Bertou Feb. 3, Hawkins June 23, Streicher Jan. 3, Anicetti June 7,

thicknessjbeing 10.2 

1. A METAL RETORT FOR THE PRODUCTION OF ALKALINE EARTH METALS BY THERMAL REDUCTION UNDER REDUCED PRESSURE, ADAPTED TO RESIST COLLAPSE IN A HEATING FURNACE WHICH COMPRISES A CAST ELONGATED CYLINDER HAVING AN INTEGRALLY FORMED CLOSURE AT ONE END AND A REMOVABLE CLOSURE AT THE OTHER END, THE INTERNAL SURFACE OF THE RETORT BEING FREE FROM DROSS AND THE RATIO OF OUTSIDE DIAMETER OF THE RETORT TO ITS WALL THICKNESS BEING 10.2 TO 13.0 THE REDUCING PORTION OF THE RETORT BEING AT LEAST 90 INCHES IN LENGTH AND HAVING AN OUTSIDE DIAMETER NOT SUBSTANTIALLY LESS THAN 12 INCHES. 